Philippine Journal of Science BOOK REVIEW 149 (2): 471-473, June 2020 ISSN 0031 - 7683 Date Received: 13 Feb 2020

Water Resources Systems of the : Modeling Studies§

Rex Victor Cruz

College of Forestry and Natural Resources University of the Philippines Los Baños, Philippines

The Philippines has abundant water resources. There is, To robustly understand how the ever-growing complexity however, a growing trend of water supply shortages in of the natural and human systems influence water major urban centers in the country—including Metro resources systems—particularly watersheds, hydrological Manila. Uneven population distribution, along with processes, water supply systems, and water demand climate change and deteriorating condition of watersheds, management—systemic and integrated approaches is some of the major drivers identified (Gleick 2013; and tools are indispensable. In view of the foregoing, Chang et al. 2013; Schnoor 2015, as cited by Rola et this book is a timely reference on the use of models al. 2015). On one end, climate change and population as a tool for integrative analysis and management of growth increase the demand for water. On the other water resources systems in the Philippines. While the end, climate change and watershed degradation increase use of models in water resources management is not a the uncertainties in the availability of water resources common practice in the country, this book highlights that makes the task of achieving water security more the potential applications of models in water resources challenging than it is already. Forecasting and balancing management in the Philippines. The book presents cases of future demands and available water resources are more of model application in various aspects of water resources complicated now than it used to be. Bringing water to management and administration. where it is needed requires a robust understanding of how much water is available and how much is the demand for In Chapter 3, the book presents an overview of the it. In the past forecasting, water availability and demand applications of models in the Philippines in science and were simpler than it is now. Understanding available water information-based policy and decision-making. Samples then was based mainly on physical factors (i.e. climatic of applications of models for solving optimization and watershed geomorphic features) while demand was problems are also described in this chapter. From Chapter conveniently evaluated based mainly on population 4–11, the book illustrates specific applications of models and economic growth. Today, the availability of water in water resources systems in the Philippines. resources is additionally influenced by land use and land Chapter 4 discusses two cases of model application in cover change, and climate change while water demand is surface and groundwater assessment in two major river further influenced by policies and development controls basins. The Pampanga and Basins are vital governing urbanization and industrialization (Rola et al. sources of water for the irrigation of vast rice production 2015). Consequently, it is now imperative to use—when areas. These river basins, however, are facing challenges available and practical—tools that are able to generate to its ability to supply irrigation water sustainably amid vital information on water availability and demand based increasing demand in the domestic and industrial sectors. on an array of biophysical, socioeconomic, and politico- In these cases, models were used to estimate the long- institutional factors. term average surface and groundwater resources as the basis for balancing supply and demand. For surface water estimation, the Sacramento model was used while §TABIOS GQ. 2020. Water Resources Systems of the Philippines: MODFLOW was used for groundwater assessment. Modeling Studies. In: World Water Resources, Vol. 4. Singh VP ed. The results of the model runs were also used to identify Basel: Springer Nature Switzerland AG. potential sites for hydropower generation.

471 Philippine Journal of Science Cruz RV: Water Resources Systems of the Vol. 149 No. 2, June 2020 Philippines: Modeling Studies

Optimization-simulation studies in two existing and on flooding was studied using two models. The UNET one proposed multi-purpose reservoirs are discussed model—a one-dimensional, unsteady flow model through in Chapter 5. The existing Angat and Upper Agno a network of open channels—was used to simulate Reservoirs—along with the proposed Agos Reservoir streamflow behavior. To simulate the storm rainfall, system—are all intended for hydropower generation, a stochastic, space-time rainfall model based on the water supply, and flood control. The Sacramento and Neyman-Scott process was used. WATPOW models were used in these three cases. As it is the task of optimizing the use of water resources in Angat The HEC-RAS model—an unsteady flow, network and Upper Agno as is expected in the proposed Agos hydraulic model—was used to quantify the extent of Reservoir is challenging that becomes more daunting with flooding in the Pasig- during TS Ketsana the dynamically shifting demands for water across sectors in 2009. In addition, the SWATCH model—a physically- and hydrological processes governing water availability. based, continuous simulation watershed model—was used Specifically, these cases illustrate how models can be to calculate the flood hydrograph. The results of these used for optimum reservoir operations such as in setting simulations showed the flood stages in various locations schedule of releases and gate openings. along the Pasig-Marikina River that are a useful basis for retrofitting existing infrastructures, e.g. bridges, and Application of models in sedimentation studies in the boosting flood mitigation measures currently in place proposed Balog-Balog Reservoir and in the existing San among other applications. Roque and Pulangi Reservoirs are reported in Chapter 6. The optimization-simulation model used in Chapter A 2-D flood inundation model with inflow flood 4, together with the Sacramento model, was used for hydrograph calculated using the Sacramento soil moisture the Balog-Balog Reservoir to determine the better accounting model was used to generate information that option between building a single high dam and multiple is a good basis for determining the best flood mitigation dam construction. The outputs of the modeling studies options for the lower Cagayan de Oro River Basin, which were used to minimize irrigation water supply deficits, experiences flooding during heavy rainfall events. maximize hydropower generation, and minimize spills. The 2-D flow and sediment hydraulic model was used to For the San Roque Reservoir, the two-dimensional (2- simulate the erosion pattern of reservoir sediment deposits D) flow and sediment transport hydraulic model was after planned and unplanned dam breaks. The modeling adapted to study the impacts of sedimentation on the study on planned dam break or removal was hypothetical reservoir operations, hydropower generation, and overall to illustrate how reservoir sediment deposits will erode service life of the reservoir. The 2-D hydraulic model during dam removal. The accidental dam break in the was also used in the Pulangi Reservoir to determine Butas Dam and the subsequent volume of sediments that the effectiveness of sediment flushing operations under were eroded from the dam and transported downstream various water inflow and water level conditions, and the was simulated using the same model. Results of simulation corresponding optimum sluice gate openings. of dam breaks are useful in implementing appropriate For comprehensive water quality studies in anticipatory mitigation measures to minimize, if not totally and Laguna Lake, various models were used (Chapter avoid, damages to life and property in case of dam removal 7). The Sacramento soil moisture accounting model with and accidental dam failure. overland and channel flow routing models were used A sample application of the enhanced EPANET model to simulate streamflows coming down from the major with the COMPLEX optimization algorithm is presented watersheds draining to Laguna Lake and Manila Bay. To below for model calibration to a portion of the pipe calculate the depth and velocities of incoming flows to the distribution network of MWSI located south of Manila bay and the lake, the hydrodynamic/hydraulic model was is discussed in Chapter 9. The results of this sample used. For describing the movement and evolution of water application illustrate the ease and efficiency in model quality in the bay and the lake, an advection-dispersion calibration and estimation of demand patterns of an model was used. The comprehensive water quality study actual pipe network problem using the said models. illustrated in this chapter highlights a robust approach for Other applications of the models, such as in monitoring addressing concerns on water quality in bays and lakes and surveillance of non-revenue water and pipe network aided by modeling. studies, were mentioned in this chapter. In Chapter 8, modeling studies in three areas and one dam Chapter 10 discusses the use of the Sacramento soil break study in the Butas Dam of Cavite are discussed. moisture accounting model along with the WATPOW Specifically, modeling was used to generate information model with the COMPLEX optimization in assessing the that is needed for precision flood mitigation. In the potential impacts of climate change on the reliability of Pasac Delta, the influence of storm rainfall movement two important reservoirs in two major river basins. The

472 Philippine Journal of Science Cruz RV: Water Resources Systems of the Vol. 149 No. 2, June 2020 Philippines: Modeling Studies models were used to assess the impacts of future climate The book, to some length, cited other models that were on the reliability of reservoir operations in the Upper Agno used in previous studies not described in this book and River Basin. In particular, the hydropower generation of presented guiding discussions on how to determine the three reservoirs along Agno River under the current the models that are appropriate for a particular case. climate was compared with that of the 2050 climate. The The various studies conducted by the author are good same models were used to assess the impacts of climate in illustrations of what models may be considered in 2050 on the reservoir sedimentation in Angat River Basin generating information that is vital to making science- and how it will affect the reliability of water deliveries based, water resource system-related decisions. and hydropower generation. The applications of modeling in assessing water quality in Subic Bay and Novaliches Reservoir are presented in REFERENCES Chapter 11. The water quality in Subic Bay was assessed using the SWATCH watershed model to calculate the CHANG H, JUNG I-W , STRECKER A, WISE D, inflows of water from upstream into the bay. The three- LAFRENZ M, SHANDAS V, MORADKHANI H, dimensional (3-D) Princeton ocean model was used to YEAKLEY A, PAN YD, BEAN R, JOHNSON G, calculate the water depths and velocities. To assess the PSARIS M. 2013. Water supply, demand, and quality water quality advection-dispersion model was used based indicators for assessing the spatial distribution of water on the estimated water depths and velocities. Particularly, resource vulnerability in the Columbia River Basin. the models were used to simulate the movement and Atmosphere-Ocean 51(4): 339–356. describe the spatial distribution of biological oxygen GLEICK PH. 2013. A drop in the bucket. Finance and demand (BOD) for various wastewater for the base case Development 50(3). Retrieved on 15 Aug 2016 from and three future scenarios of BOD loadings depending http://www.imf.org/external/pubs/ft/fandd/2013/09/ on the reduction measures adopted. Likewise, the models gleick.htm were used to simulate the oil spill movement of an actual oil spill incident in Subic Bay. ROLA A, PULHIN J, ARCALA-HALL R. 2015. Water Policy in the Philippines: Issues, Initiatives and Pros- The FEMWATER is a 3-D saturated-unsaturated, pects. Springer-Verlag. finite-element groundwater flow and contaminant transport model that was used to assess the potential SCHNOOR JL. 2015. Water unsustainability. Daedalus, risk of contaminating the Novaliches Reservoir through the Journal of the American Academy of Arts & Sci- groundwater flow and pollutant transport from the Payatas ences 144(3): 1–11. Dumpsite. While the results of this study showed that the risk of contaminating the Novaliches Reservoir is nil, the potential application of the models in the proper location of dumpsites in relation to existing and potential reservoirs is illustrated. The book closes with Chapter 12 covering five major groups of topics related to modeling in water resources systems. The chapter compares the scientific and data analytic approaches to and the importance of integration of geomorphological, ecological, and hydrological interactions in water resources modeling. It also covers the importance of monitoring and data collection as well as of decision support tools in promoting science-based management of water resources in the Philippines. The chapter discussion ends with the importance of holistic and transdisciplinary approaches to water resources management, together with building urban resilience to water-related disasters. Overall, this book is a good reference for water resource system managers and practitioners, students, researchers, and academics on the applications of models in various water resource system related studies in the Philippines.

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